1. Field of Invention
The present invention relates to an ion adsorbent capable of efficiently removing harmful ions in water, wherein the processability and yield in the granulation are improved.
2. Description of Related Art
With the severe regulations for environmental safeguard, an adsorbent capable of removing phosphate ions and fluoride ions effectively in waste water has been required. However, since water is a good solvent for many compounds, particularly salts, it is not easy to separate and remove the compounds and ions, which were once dissolved in water, from an aqueous solution.
As a method of separating/removing harmful metal ions such as copper ions from an aqueous solution containing them, there has been suggested a method of recovering copper ions as metal copper using a metal having ionization tendency larger than that of copper, such as aluminum (Japanese Patent Kokai Nos. 68428/1976 and 26366/1977). However, it is difficult to recover copper from an aqueous solution containing copper ions in low concentration such as 10 ppm or less.
On the other hand, as a method of removing phosphate ions as one of causative substances for eutrophication, there is a so-called flocculation sedimentation method, comprising adding chemicals containing metal ions such as calcium ions, aluminum ions, etc. to waste water containing phosphate ions to remove the phosphate ions as hardly soluble phosphates. Nevertheless, this method, which produces large quantities of sludge and therefore causes the secondary environmental pollution, is not necessarily regarded as a satisfactory one.
It has been known that hydrates of titanium oxide, zirconium oxide and tin oxide possess the property of ion exchange and, for example, in acidic solutions, through the fixing of hydrogen ions, H.sup.+, become anion exchangers with a capacity for absorbing phosphate ions, fluoride ions, sulphate ions, nitrate ions, nitrite ions, chloride ions, arsenate ions, arsenite ions, chromate ions and molybdate ions. It has also been known that in an alkaline solution, the hydrates function as cation exchangers, through the fixing of hydroxyl ions, OH.sup.-. In order to improve the strength of the adsorbent with paying attention to the ion exchange property of these metal oxide hydrates, there is suggested an adsorbent which is prepared by mixing hydrated ferrites of titanium, zirconium or tin with an unsaturated polyester resin or a polyurethane resin and curing the mixture (Japanese Patent Kokai Nos. 118734/1981 and 50543/1982).
Use of these metal hydrated ferrites packed in a column as powders causes large pressure loss and clogging, and further consumes a great deal of times, efforts and costs for a treatment after ion adsorption, for example, filtration, separation and regeneration of the adsorbent. An adsorbent prepared by mixing powders of a metal hydrated sulfate with an unsaturated polyester resin, followed by molding has such drawbacks that the intrinsic ion exchange capacity of the metal hydrated ferrite is not sufficiently exhibited and the adsorption rate becomes slow. Both cases had problems in view of the efficiency of removing ions and facilitation at working. Furthermore, since these resins are generally used in combination with an organic solvent, the working environment was also poor.